Slide rule



Aug. 24 1926.

H. Rrrow SLIDE RULE Filed Deo. 22

. 1923 .'5 Sheets-Sheet 1 N KJ SKI,

N VENTOR Aug. 24, 192s. 1,597,483

H. RlTow.l

SLIDE RULE Filbed Dec. 22I 1923 5 Sheets-Sheet 2 Aug. 24, 1926.

H. RITOW SLIDE RULE Filed Dec. 22, 1925 5 Sheets-Sheet` 5 N m m msm N mr ANN L 2 c y m B Q W w it n nm 7 x m C l L T. c w1 T9 M 2 u C non :wmwzzmuw-m-:lz-m- WU. M mmm; .wm |0 F B B MUY?! l 5. n v D (1 Q wmjgom. OnMOOv n f F 8 L c L i a DU L L. m F L M @i12- C wm mr 7n C :wmrzmdzrv: ME mE FIG. 8

. NVENTOR.

. sett-ing vPatented Aug. 24, 1926.

UNITED STATES 1,597,483 ,PATENTl oFFlcE.

HERMAN RITOW, OF CHICAGO, ILLINOIS, ASSIGNOR T0 THE FREDERICK POSTICOM- PANY, 0F CHICAGO, ILLINOIS,A

SLIDE A CORPORATION OF ILLINOIS.

RULE.

Application filed December 22, 1923. Serial No. 682,363.

The present invention has relation to an\ improvement in `that class of mathematical sliderules in which a cylindrical body rotating about an axis is provided with a helical. "logarithmic scale and of which a typical example is the well known Fullers sliderule.

The object of the present invention is to provide an improved cylindrical sliderule of very great accuracy and of simple and easy operation. The Fuller rule has great accuracy but is clumsy to handle. All the other sliderules for great accuracy such as the Thacher sliderule are large, unwieldly and evenconfusing. I attain this object by a novel arrangement of two rotating cylinders, each provided with helical and with circular logarithmic scales, as illustrated in the accompanying drawing, in which Fig. 1 is a longitudinal section through ythe device showing the method of construction,

Fig. 2 is a top view ofthe sliderule showing the ylocationof the logarithmic scales,

Fig. 3 is a section at right angles to the axis taken between the two cylinders, on line 3--3,'Figs. 1 and 2, l

Fig. 4 is a crosssection through a cylinder on line 4 4, Figs. 1 and 2 Fig. 5 is a view to enlargedscale showing part, of the scales B for the first setting of both cylinders to find the product of 7.5632y by 1.27133.

Fig. 6 is a vieW to part of the scales B for the second setting to find the product of 7 .5632gby 1.27133.

Fig. 7 is a view to enlarged scale showing part of the scale C for the third setting to dfind the product of 7.5632 by 1.27133, an i Fig. 8 is a view to enlarged scale showing part of the scales C for the fourth and last to lf ind the product of 7.5632 4by 1.27133. l

Similar numerals and letters refer to similar parts throughout the four views. The integral parts of the improved sliderule are the axle 1, the rotating cylinders 2, the index rod 3,'the clamps 4 and 5, the spring boxes 6 and the springs 7. y

'By pulling either springbox 6 towards the nearby clamp 5'the adjoining cylinder 2 is free I11:0 rotatesmoothly arund the axle 1. The springbox 6 when not pulled towards the-clam 5 keeps the adjoining c inder 2 inany esired position. The 1n ex enlarged scale showing rod 3 is provided with a crosspiece that fits snugly around the axle 1. The clamps 4 are screwed tightly to the axle 1 on each side of sald crosspiece so that the index rod 3 is held firmly in any given position by friction with the two clamps 4, and so that whenV desired the index rod can be moved by pushing on the handle 8 connected to the indexrod 3, the two clamps 4 not being placed so tightly against` the crosspiece as to prevent the forced motion of the index rod. The twoy clamps 5 are screwed tightl to the ends of the axle 1. The spring 7 is geld between the clamp 5 and the spring box 6 so that the spring pushes the spring box againstthe cylinder '2, keeping the latter, in any fixed position so long as the spring box 6 is not drawn towards the clamp 5. Clamps 4 and 5 are provided with screws with which said clamps can be tightened to the axle 1.

Each of the cylinders 2 is provided with three scales, A, B and C, marked on the c lindrical surface. Scale A is a uniform subdivided scale, rthe subdivisions being al equal. Scale `B is a logarithmic scale of the length of the circumference of the cylinder exactly equivalent to the D scale of the Mannheim rule and Wound just once around the cylinder. Scale C is a helical scale of many times the length of the circumference of the cylinder and helically wound around the cylinder.

The index rod 3 is provided on each side with a uniform scale, each of whose smallest subdivisions corresponds to thepitch of the helix of scale C. The subdivisions are numbered so that the cylinder length of the helix ,is divided into'ten equal parts and numbered from 0 to 10. Scale A in its entiretyfurther subdivides the smallest sub` division of the index rod scale..

To perform a multiplication `four steps are made as illustrated in Figs. 5, 6, 7, 8.

First the index or scale of the left vhand site one factor on the cylinder. Fig. 5 shows the 1 B scale opposite the reading 1271 right B scale.

The second till its edge covers the reading `of the second factor on the B scale of the left cylinder. The preliminary answer is found under the edge of the index rodon the B scale of the right cylinder.

c lindei` is sete po- BY scale of the right of the left onl the step is to turn the index rodA 1 reading of the B 'l Fig. 6 shows the setting for this second reading of the C soa e of the left cylinder and turning the right cylinder till one factoon is directly under the edge of the index r Fig. -r`7 shows the index rod edge directly over 1 on the C scale of the left cylinder and directly over 1.27133 on the C scale of the right cylinder.

The fourth and last step consists of turning the index rod till its edge covers the second factor on the C scale of the left c linder. The answer is then picked out rom the many readings of the right cylinder C scale by finding the particular readin closest to the approximate answer^ foun from the first two ste s.

Fi 8 shows the index rod ed covering t e second factor 75632 on the scale of the left cylinder and shows the index rod edge covering many numbers on the C scale of the\ right cylinder. The three nearest to the approximate" answer 962 are 91896, 96153 fand 100685. It is evident that the nearest answer is 96153 and this answer checks with the ap roximate answer within 1,4 per cent as it shjould.

It is readily seen that the third and vfourth steps (Figs. 7 and 8) differ from the rst two (Fi 5 and 6) only in thefollowing:

The scales are used in place of the B scales and the answer is picked out with the help of that obtained fromsteps 1 and 2. It is also readily seen that ste s 1- and 2 are identical with the steps of or inary multiplication as performed on the Mannheim sllde rule., The left cylinder takes the lace of the slide, the ri ht cylinder that o the body, the index ro is used like the indicator, the left B scale corresponds with the Mannheim C scale and the right B scale corresponds with the Mannheim D scale.

Division likewise is erformed in four steps, as illustrated by Figs. 6, 5, 8 and 7.

hese steps are the reverse of those used in multiplication. First the divisor on the left B scale is set o osite the dividend, on the right B scale. hus in Fig. 6 we have the The divisor 756 is set on the left B scale opposite the dividend 962 on the right B scale. In step 2 we turn the two cylinders toffether till the 1 or index reading on the let B scale can be seen and find the approximate answer on the right B scale opposite the 1 orindex reading on the left B scale.

In Fig. 5 we find the approximate answer to be 1271. The third and fourth steps consistof a repetition of the first and second except that we use the C'scales in place of the B scales and that we must use the index rod and the approximate answer to pickvout the accurate answer. Thus in Fig. 8 the divisor 75632 on the left C scale is placed simultaneousl under the index rod edge with the' dividzend 96153 on the rightC scale, and in Fig. 7 the index rod has been turned to cover 1 readingor index of the left C scale. It covers simultaneously on the right C scale the numbers 121411, 127133 and 133125. The nearest to the approximate answer is 127133 and this checks with the former to 1/4 per cent as it should.

It is readily seen again that the operation of dividing is almost identical with that used om the Mannheim slide rules.

To find vthe logarithm of a number, turn either cylinder till the desired4 number is under the edge of the index rod. Read the .rst two digits of the logarithm on the index rod adjacent to the graduated'edge of the number and read the last three or more digits on the A scale under the edge of the index -rod. Thus in Fig. 8 the logarithm of 96153 is read .98 on the index rod and on the A scale we read 296. The logarithm is, therefore, .98296.

It is to be noted that ever accurate computation with the improve sliderule contains within itself a check to the accuracy of the preliminary computation with the B scales. This c eck being absolutely independent of the final operation, the computer as the' certainty that his answer iscorrect. If a mistake is made in either the prelimi- `naxy or the accurate computation, no number un e r the indexrod will agree with the first preliminary. answer and the computer knows e must repeat the computation. This makes the improved sliderule a very advantageousv one for those who desire accuracy and considering the great simplicity of operating with the new sliderule it should appeal to the large classl of merchants who have been asking for specially accurate and simple sliderules.. K

In' my Patent No. 1,405,333, patented January 31, 1922, I show a sliderule whose -accuracy can be raised to ten or even twenty times that of the ordinary Mannheim rule, this being done with the help of folded logarithmic scales, placed on the body and slide of the usual type of slide rule. My new improved sliderule described in this specification can easily be made for an accuracy of computation of fifty, one hundred or even one thousand times the accuracy of the ordinary Mannheim rule, this being 4done withthe help of helical logarithmic lscales, placed on two adjoining, freely rotatmg cylinders with a special index rod.

Of all the rules onthe market the Fuller sliderule is the nearest to my rule in accuracy,

l sited markin its helical scale being any ames the length of the usual. Mannheim rule. Its

clumsy operation with its one sliding and ro' tating cylinder and its ,three indices'make it man times slower to work wlth than my rule without anycheck to give the operator certainty of correctness.

On account'of the easek with which the cylinders can be turned in my improved slide.- rule as well as stop d and kept at an de.-

un er the index r the double cylin rica-l form of sliderule described in this specification is a very convenient o ne even for the elementary form of- Mannheim scales.l The cylindrically wound Mannheim scale has the added advantage of being continuous without any beginning or end thus making comptation with the cylindrical scales a simpler and quicker operation. i

' I claim as new and desire to secure with Letters Patent A LA slide rule comprising an axle, two cylinders and an index rod rotating about said axle, said cylinders being each provided with twol logarithmic scales, one of said scales beingnot longer than the circumference of the cylinder, the other being wound many times aroundthe cylinder; said two Y cylinders and index rod coordinating in such wise that computation may vfirst be performed with the short 'logarithmic scales, then repeated lwith the longervlogarithmi'j scales, 4the more accurafjanswerf.-being picked from the longer. wound scale's-f-'witlxjthe help of the answer first found' with the shortlogarithmic scales.

2. A slide rule comprising an axle, two cylinders and an index rod rotating about said axle, said cylinders being each' prof vided with two logarithmic scales, one of said scales beingnot longer than the circumference of the cylinder, the other being wound-,many times around the cylinder; said cylinders and index rod being provided each with uniformly divided scales for the determinationl of the logarithms of numbers; said two cylinders and-index rod coordinating in such wise that computation may first be performedwith the short `logarithm scales, then'repeatedwith the 'longer logarithmic. scales, the more accuratev answer being picked from the longer wound scales with the help of the answer first found with the short logarithmic scales.

3. In a slide rule@ comprising` two iconcentric'cylinders, means for mounting them in fixed relation so that they may be free to rotate with respect one to the other, separate logarithmic scales wound spirally, a number of them about each cylinder, and separate logarithmic scales wound once about each cylinder, an index rod-parallel with theI axes of the cylinders and mountedy for movement along their peripheries about their axesTYt-he index rod havingv a pair of scales one for each cylinder extending throughout the entire length of so much of 'the cylinders as carries the Ispiral scale, the

divisions on the rod being equal. y

, 4. A slide rule comprising two cylinders mounted for rotation about the same axis and arranged end to end, an index rod mounted for rotation about their common scales, the more accurate answer being picked from the longer wound scales withr the help of the answer first found with the short logarithmic scales.

, -51'AL slide rule comprising two cylinders 'mounted for rotation about the nsame axis and arranged end to end, an index rod mounted for rotation. about their common axes, said cylinders being eachyprovided with two logarithmic scales, one of said scales being not longer-than the circumference of the cylinder, the other being wound manyitimes around the cylinder; said cylinders and index rod being provided each wtih uniformly. divided scales for the determination ofthe logarithms of numbers; said two cylinders and index rod coordinating in such wise that computation may first be peformed with the short logarithmic scales, 'then repeated with the longer logarithmic scales, the more accurate answer beingicked from the longer wound scales with the help of the answer lirst found with the. short logarithmic scales.

In witness whereof I sign '-my'name,"

November 30, 1923.

` HERMAN RITQW; 

